The present invention relates to an image display apparatus for displaying data in computers, facsimiles and the like, and more particularly to an apparatus comprising a repetitively usable image bearing web in the form of an endless belt on which an image can be formed and which can be moved to display the image.
Image display apparatuses for displaying data in computers, facsimiles and the like are generally of a cathode ray tube (CRT) type. In place of such image display apparatuses, the applicant has proposed an image display apparatus which comprises an image bearing web in the form of an endless moving belt.
The image display apparatus proposed by the applicant is shown in FIG. 1 which comprises a casing 1 and an endless belt-shaped photosensitive web 8 movably mounted within the casing 1. The photosensitive web 8 is intermittently driven by drive means (not shown) and guided by guide roller 9, 10, 11 and 12. There is provided a semiconductor laser (not shown) which is adapted to generate output light beams modulated by electric image signals. The output light beam impinges on the inner face of the photosensitive web 8 and scan in one direction the same by a scanner 5 through a f.multidot..theta. lens 6 and mirror 7. The photosensitive web 8 may be consist of a transparent, electrically conductive substratum and a photoconductive layer formed thereover.
In an exposure position A, a development device 15 is disposed opposite to the outer face of the belt-shaped photosensitive web 8 and comprises a sleeve 17 within which a magnet 16 is mounted to rotate in the direction shown by an arrow in FIG. 1. An electrically conductive and magnetic developer (toner) 18 is supplied to the surface of sleeve 17 and will contact with the surface of the photosensitive web 8 after toner 18 has been uniformly regulated as a layer by a blade 19. DC voltage is applied across sleeve 17 of development device 15 and the substratum of the photosensitive web 8. Adjacent to the exposure and development position there are located rollers 13 and 14 which serve to maintain photosensitive web 8 flat so that the gap between the photosensitive web surface and sleeve 17 of development device 15 will exactly be kept constant. An image is written on surface photosensitive web 8 in the position A by the use of light beam and then developed into a toner image which will be fed to a display section 2.
Display section 2 includes a rectangular window 3 formed in the front face of the casing 1 and a transparent member 4 mounted over window 3 through which the toner image on photosensitive web 8 can be observed externally.
Photosensitive web 8 may be stopped automatically or manually for a given period of time if a predetermined location thereof on which the visible image is formed reaches the region of window 3. In this manner, the toner image on photosensitive web 8 surface can be observed at window 3 through transparent member 4.
The image display apparatus further comprises a lamp 20 for erasing any hysteresis which possibly remains on photosensitive web 8. Lamp 20 is in its ON state only when photosensitive web 8 is being moved, and it is turned OFF with the stop of web 8.
FIGS. 2 and 3 illustrate the principle of image formation which is used in the image display apparatus shown in FIG. 1.
FIG. 2 shows the state of charge in the bright area of information light. When toner 18 contacts photosensitive web 8 while a voltage is being applied to toner through sleeve 17, an electrical field is applied to photoconductive layer 8c. At this time, if the information light is projected, photocarriers e are produced in photoconductive layer 8c and then moved to near the surface of photoconductive layer 8c under the action of the electric field. As a result, a strong electrostatic attraction force acts between toner 18 and photoconductive layer 8c so that toner 18 will be deposited on photoconductive layer 8c, that is, the surface of photosensitive web 8.
In the illustrated apparatus, photoconductive layer 8c is of an N-type semiconductor, while a positive voltage is applied to toner 18. Photo-carriers e, which have been produced near the substratum in photoconductive layer 8c on the irradiation of the information light LB, can satisfactorily be moved toward photoconductive layer 8c. As a result, toner 18 can be deposited on photosensitive web 8 under the action of the strong electrostatic attraction force between toner 18 and photosensitive web 8.
FIG. 3 shows the state of charge in a dark area. When an electric field is applied across toner 18 and a transparent conductive layer 8b of the substratum, an electrostatic attraction force is produced therebetween. However, this electrostatic attraction force is relatively small since toner 18 and conductive layer 8b are spaced away from each other by photoconductive layer 8c. Toner 18 is therefore forced to separate from photoconductive layer 8c, that is, photosensitive web 8 due to various causes such as the magnetic force of rotating magnet 16 within fixed sleeve 17, and attracting force acting among particles in toner 18 and so on.
If it is desired to effect the change of toner image on photosensitive web 8, a new image can be formed thereon simply by causing photosensitive web 8 to pass by the exposure and development position. In other words, if the toner holding portion of photosensitive web 8 is to be changed to a non-toner-holding portion, the electrostatic attraction force of toner 18 is reduced because of the no absence of light application and the elapse of time, and toner 18 is removed from photosensitive web 8 under the influence of the magnetic field in magnet 16 to provide an area having no toner 18. On the other hand, if the toner holding area of photosensitive web 8 is to be kept as it is, photo-carriers e are again injected under the action of information light so that new toner 18 will be attracted to photosensitive web 8 against the action of the magnetic field to keep toner thereon. Thus, toner 18 image on photosensitive web 8 will not influence the subsequent formation of an image. This means that an additional cleaning apparatus is not required in image display Section 2.
As shown in FIGS. 2 and 3, image display Section 2 further comprises a polyethylene terephthalate film 8a supporting conductive layer 8b and a source of voltage E for sleeve 17.
As another system for displaying a given image on an image bearing web in the form of an endless belt which is intermittently moved, there is a thermal recording system comprising a reversible heat-sensitive recording web in the form of an endless belt formed, for example, of Ag.sub.2 HgI.sub.4 which is a compound of silver, mercury and iodine, and a thermal recording head used as image formation means.
In the aforementioned arrangements of the image display apparatus, the image bearing web in the form of the belt-shaped photosensitive or heat-sensitive web on which an image is to be formed is repetitively usable and bears such images at substantially the same area or areas, so that the web includes at least one image-forming area and one non-image-forming area. The image-forming area is subjected to the image light at the image exposure position A and comes to bear the toner image and then receives external light through the window 3 at display Section 2, so that the image-forming area comes to show a hysteresis which is different from that of the non-image-forming area. If the area on which images are frequently formed and the area on which images are not frequently formed are both contained in one image on display, the difference in the hysteresis property may appear as a difference in the quality of the image within the one image. More particularly, where a fixed area of the image bearing web is repetitively used to display or form images thereon, the photosensitive layer of the image bearing web may adversely be affected partly by the light through the display section or the information light if the image bearing web is photosensitive. If the image bearing web is heat-sensitive, the heat-sensitive layer thereof may adversely be affected partly by temperature keeping means. If such an image bearing web that has been so affected is stopped at a shorter interval than the predetermined, and then moved through the predetermined length, the portion of the image bearing member on display through the window 3 will contain both an area influenced by the light and another area which has been used to provide a spacing between adjacent images and an approach run and which has not been influenced by the light, there will be provided different qualities in one image.